Ask the Doctors: Taking too many vitamins can have side effects
A: Thank you for the opportunity to explore this topic. As you might imagine, I encounter many people who are dubious of the medications, treatments and advice that doctors have to give, but who also take remedies that haven't been studied or who take vitamins at excessive dosages with a blind disregard to potential side effects.
Let's begin with vitamin B6. This crucial vitamin is involved in metabolic processes that help the formation of glucose, heme, niacin and neurotransmitters in the body. Many foods contain B6, including pork, turkey, beef, eggs and potatoes, breakfast cereals, bananas, nuts, beans and peas. Deficiency of B6 is rare, but when it happens it can lead to inflammatory conditions of the mouth, irritability, confusion, depression and, rarely, nerve dysfunction in the legs and arms. People with severe deficiency can develop seizures. Some medications (Sinemet for Parkinson's disease, hydralazine for high blood pressure and isoniazid for tuberculosis, for example) can lead to B6 deficiencies, as can alcoholism, diabetes, asthma and lymphoma.
Requirements for B6 vary for different age groups, from 1 milligram per day in children to 1.7 milligrams per day in men over the age of 50. If you have a balanced diet, you should be able to get this daily intake of B6 from the foods you eat. B complex supplements can contain 2 to 10 milligrams of B6, with some people taking formulas containing ridiculously high levels. That may not seem like a big deal, but too much B6 can cause nausea, dizziness and nerve dysfunction in the legs and arms, leading to burning, tingling and numbness.
Another B vitamin, niacin, can cause liver and muscle inflammation when taken at doses greater than 3,000 milligrams.
Keep in mind that the list of potentially problematic everyday vitamins neither starts nor stops with the B vitamins.
Vitamin C: In those predisposed to kidney stones, vitamin C at high doses increases the risk of them.
Vitamin D: The recommended intake for vitamin D, which is important for bone mineral density and overall health, is about 600 to 800 units per day. However, manufacturers make — and some practitioners recommend — doses up to 10,000 units daily. Unfortunately, chronic intake of high doses of vitamin D can lead to a loss of bone density, calcium deposition in the kidneys and muscle pain. Those who take even higher doses of vitamin D can have severe elevation of calcium in the blood, which can lead to confusion, vomiting, poor appetite and muscle weakness.
Vitamin A: This vitamin is necessary for visual health, and deficiency (rare in the United States) leads to night blindness and even complete blindness. Recommended daily intake of vitamin A is 2,300 to 3,000 units. However, some people take more than 30,000 units per day, which can lead to liver toxicity, muscle and bone pain, vision problems, and coordination and balance difficulties.
This is just a starter list of examples of toxicity linked to high vitamin doses. If you have an illness that can lead to vitamin deficiencies, checking your blood vitamin levels — and potentially adding supplements — is appropriate. But most people need a reminder that blindly taking high doses of vitamins can lead to unnecessary side effects; you're to be commended for looking for information on labels. When it comes to vitamins, more is not always better.
Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.
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